Venous pressure measurement apparatus

ABSTRACT

A non-invasive venous pressure measurement apparatus is provided, including: a first cuff attached to a portion including a vein and an artery in a living body; a pressure control unit that changes a first applied pressure applied by the cuff to the portion; a pulse wave detection unit that detects a pulse wave from a pressure received by the cuff from the portion; another pulse wave detection unit that detects another pulse wave including at least an arterial pulse wave in another portion of the living body; an analyzing unit that analyzes a correlation between the two pulse waves, which are changed as the applied pressure is changed by the pressure control unit changes; and a venous pressure calculation unit that calculates a venous pressure based on the applied pressure and a result of analysis by the analyzing unit.

CROSS-REFERENCE TO RELATED APPLICATION

This applicationMore than one reissue application has been filed for thereissue of U.S. Pat. No. 9,743,846. The reissue applications are thepresent application, which is based ona divisional of U.S. applicationSer. No. 16/397,760 filed Apr. 29, 2019, in the U.S. Patent andTrademark Office, and U.S. application Ser. No. 16/397,760, which isalso a reissue application of U.S. Pat. No. 9,743,846, which was filedas U.S. application Ser. No. 13/433,708 on Mar. 29, 2012, in the U.S.Patent and Trademark Office, which claims priority from Japanese PatentApplication No. 2011-074839 filed on Mar. 30, 2011, the contents ofwhich are incorporated herein incorporated by reference.

BACKGROUND

1. Technical Field

Embodiments include a venous pressure measurement apparatus, andparticularly, to a venous pressure measurement apparatus fornon-invasively measuring a mean venous pressure.

2. Description of Related Art

The venous pressure in the vicinity of the right atrium is called acentral venous pressure, which indicates a cardiac preload used as animportant index to recognize the circulatory dynamics.

The central venous pressure can be invasively measured by inserting acatheter into the vicinity of the right atrium. However, recently, avenous pressure measurement apparatus capable of non-invasivelymeasuring the central venous pressure with a reduced burden to thepatient has been developed.

In Unexamined Japanese Patent Publication No. 2010-279654 (“JP2010-279654”), there is disclosed as related art of the non-invasivevenous pressure measurement, in which the artery and the vein areoccluded by a cuff applied to the upper arm once, after that, theocclusion of the artery and the vein is sequentially released bygradually reducing the cuff pressure, and, at the same time, these aredetected by using a gray scale value of a projection image obtained byirradiating infrared rays onto the leading edge of the antebrachialregion, so that the venous pressure is measured based on the cuffpressure when the congestion is released.

However, in “JP 2010-279654”, it does not teach that the venous pressureis measured while a living body is under natural conditions since thevein is congested once, and the venous pressure is measured when thevenous blood starts to flow from the congested state. In addition,instruments to irradiate infrared rays and the infrared sensor arenecessary.

SUMMARY

A non-invasive venous pressure measurement apparatus capable ofmeasuring the venous pressure using simple so instruments based on achange of the venous pulse wave while the living body is under naturalcondition is provided.

The aforementioned problems of measuring venous pressure are addressedby the following configuration.

In one aspect there is provided a venous pressure measurement apparatusincluding: a first cuff attached to in a first portion including a veinand an artery in a living body; a pressure control unit that changes afirst applied pressure applied by the first cuff to the first portion; afirst pulse wave detection unit that detects a first pulse wave from thepressure received by the first cuff from the first portion; a secondpulse wave detection unit that detects a second pulse wave including atleast an arterial pulse wave in a second portion different from thefirst portion of the living body; an analyzing unit that analyzes acorrelation between the sec- and pulse wave detected by the second pulsewave detection unit and the first pulse wave detected by the first pulsewave detection unit, which are changed as the first applied pressure ischanged by the pressure control unit; and a venous pressure calculationunit that calculates a venous pressure based on the first appliedpressure and a result of analysis by the analyzing unit.

In another aspect there is provided a venous pressure measurementapparatus including: a cuff attached to a portion including a vein andan artery in a living body; a pressure control unit that changes anapplied pressure applied by the cuff to the portion; a pulse wavedetection unit that detects a pulse wave from a pressure received by thecuff from the portion; and a venous pressure calculation unit thatcalculates a venous pressure based on the applied pressure and the pulsewave detected by the pulse wave detection unit, the pulse wave beingchanged as the applied pressure is changed by the pressure control unit.

The objects, features, and characteristics presented, other than thoseset forth above, will become apparent from the description given hereinbelow with reference to preferred embodiments illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a venous pressure measurementapparatus.

FIG. 2 is a flowchart showing a process of measuring a mean venouspressure by the venous pressure measurement apparatus.

FIG. 3 shows graphs of pulse waves in the proximal and distal locationswith respect to the heart in the upper arm and subtraction waveformsthereof.

FIG. 4 is a diagram showing a relation between applied pressure and themaximum amplitude of the subtraction waveform.

FIG. 5 shows graphs of a relation between first pulse wave and secondpulse wave on a first applied pressure value basis.

FIG. 6 is a flowchart showing a process of measuring a mean venouspressure by the venous pressure measurement apparatus.

FIG. 7 is a flowchart showing a process of measuring a mean venouspressure by the venous pressure measurement apparatus.

FIG. 8 is a block diagram showing a venous pressure measurementapparatus.

FIG. 9 is a block diagram showing a venous pressure measurementapparatus.

FIG. 10 is a flowchart showing a process of measuring a mean venouspressure by the venous pressure measurement.

FIG. 11 is a flowchart showing a process of measuring a mean venouspressure by the venous pressure measurement apparatus.

DETAILED DESCRIPTION

Hereinafter, a venous pressure measurement apparatus according toembodiments of this invention will be described in detail with referenceto the accompanying drawings.

FIG. 1 is a block diagram showing a venous pressure measurementapparatus 10 according to an embodiment. Referring to FIG. 1, a livingbody 100 is illustrated along with the venous pressure measurementapparatus 10, and a first cuff 20a and a second cuff 20b are attached toan upper arm 101 of the living body 100.

In order to measure the mean venous pressure, the venous pressuremeasurement apparatus 10 includes the first cuff 20a (first pulse wavesensor), the second cuff 20b (second pulse wave sensor), a firstpressure control unit (pressure control unit) 30a, a second pressurecontrol unit (pressure control unit) 30b, a first pressure sensor 40a(first pulse wave sensor), a second pressure sensor 40b (second pulsewave sensor), a pressure waveform analyzing unit (analyzing unit, venouspressure calculation unit) 50, a display unit 60, and an abnormalitynotification unit 65. As disclosed below in further detail, the pressurewaveform analyzing unit 50 is a device which receives pulse waves fromthe first and second cuffs respectively as electric signals.Accordingly, it will be understood by those skilled in the art that thepressure waveform analyzing unit 50 will comprise an electric circuit.As also explained below, the pressure waveform analyzing unit 50 will(2) receive pressure values (data) from the first and second pressurecontrol units 30a, 30b, (3) analyze a correlation between the pulsewaves from the first and second cuffs 20a, 20b, (4) perform calculationsto determine venous pressure, and (5) transmit waveforms and variouscalculation results to a display unit 60 (e.g., a liquid crystaldisplay). As is known, an electronic device that receives data and pulsewaves as electric signals, uses such information to analyze correlationbetween two pulse waves, performs calculations, and transmits waveformsand calculation results to an electronic display unit, is commonlyreferred by those skilled in the art as a computer, a processor or anelectronic processor circuit.

The first cuff 20a is attached by being wound around the upper arm 101in the vicinity of the axillary region which is a part of the livingbody (first portion). An attached portion is pressurized under controlof the first pressure control unit 30a, and a pulse wave (hereinafter,referred to as a “first pulse wave”) which is a vibration of thevascular wall detected as a pressure received from the pressurizedportion is transmitted to the first pressure sensor 40a. In addition,the position where the first cuff 20a is attached is not particularlylimited if both an artery and a vein exist there. The first pulse wavemay include pulse waves of the artery and the vein.

The second cuff 20b has a function similar to the first cuff 20a. Thesecond cuff 20b is attached to a portion (second portion) distal to thefirst cuff 20a with respect to the heart in the upper arm 101. Thesecond cuff 20b pressurizes the attached portion under control of thesecond pressure control unit 30b and transmits a pulse wave(hereinafter, referred to as a “second pulse wave”) received from thepressurized portion to the second pressure sensor 40b. The positionwhere the second cuff 20b is attached is not particularly limited if itis different from the attached portion of the first cuff 20a. However,the second cuff 20b is attached to the position where at least the pulsewave of the artery can be detected. Therefore, the second pulse waveincludes at least the arterial pulse wave.

According to an embodiment, the pressure applied by the first cuff 20ato the living body when the correlation between the first pulse wave andthe second pulse waves is minimized is estimated as the mean venouspressure based on a principle of the oscillometric method. Suchestimation can be made based on a fact that (1) the applied pressure bythe cuff when the venous pulse wave is maximized can be estimated as themean venous pressure since the venous pulse wave is maximized when apressure difference between the inside and the outside of the venousblood vessel is minimized, and (2) the correlation between pulse wavesin the distal and proximal locations is reduced as the venous pulse wavecomponent increases since the venous pulse wave is decreased as thevenous blood vessel becomes distal with respect to the heart with itshigh compliance.

If a pressure higher than the mean venous pressure is applied to thevein, the venous pulse component gradually decreases as the appliedpressure increases. If the vein is perfectly occluded, the venous pulsecomponent is disappeared from the pulse wave. The venous pulse componentof the pulse wave decreases even when a pressure smaller than the meanvenous pressure is applied to the vein.

Here, a backflow valve exists in the venous intravascular lumen of theextremity. The venous pulse is more strongly exhibited in the vein ofthe upper arm in the vicinity of the axillary region proximal to thebackflow valve in comparison with the vein distal to the backflow valvewith respect to the heart. Therefore, it is possible to increase adifference of the venous component between the first pulse wave and thesecond pulse wave by attaching the first cuff 20a and the second cuff20b over the backflow valve and attaching the first cuff 20a as near aspossible to the heart. As a result, it is possible to more accuratelymeasure the correlation between the first pulse wave and the secondpulse wave and improve the measurement accuracy of the mean venouspressure. Such a condition can be satisfied by attaching the first cuff20a in the upper arm 101 in the vicinity of the axillary region andattaching the second cuff 20b in the portion distal to the first cuff20a with respect to the heart in the upper arm 101.

Since the mean venous pressure measured when the first cuff 20a has thesame height as that of the heart can be considered as the central venouspressure, the central venous pressure can be measured in such a bodyposition by using the venous pressure measurement apparatus according tothe present embodiment.

The first pressure control unit 30a controls the first cuff 20a so thatthe portion where the first cuff 20a is attached is pressurized with apredetermined pressure, and the applied pressure is changed. The firstpressure control unit 30a may pressurize the portion where the firstcuff 20a is attached, for example, by sending air to the first cuff 20a.

The second pressure control unit 30b may control the second cuff 20b sothat the portion where the second cuff 20b is attached is pressurizedwith a predetermined pressure, and the applied pressure can be changed.The second pressure control unit 30b may pressurize the portion wherethe second cuff 20b is attached, for example, by sending air to thesecond cuff 20b.

The first pressure sensor 40a receives the first pulse wave transmittedfrom the first cuff 20a and outputs it to the pressure waveformanalyzing unit 50 as an electric signal. The first pulse wave receivedby the first pressure sensor 40a from the first cuff 20a is a pressurewaveform obtained by using air as a medium. The first pressure sensor40a may be a piezoelectric element for converting the pressure signalinto the electric signal.

The second pressure sensor 40b receives the second pulse wavetransmitted from the second cuff 20b and outputs it to the pressurewaveform analyzing unit 50 as an electric signal. The second pulse wavereceived by the second pressure sensor 40b from the second cuff 20b is apressure waveform obtained by using air as a medium. The second pressuresensor 40b may be a piezoelectric element for converting the pressuresignal into the electric signal.

The pressure waveform analyzing unit 50 receives the first pulse waveand second pulse wave from the first pressure sensor 40a and the secondpressure sensor 40b, respectively, and receives the pressure valuesapplied to the upper arm from each of the first pressure control unit30a and the second pressure control unit 30b, and calculates the venouspressure based on the pressure applied to the living body by the firstcuff 20a when the correlation between the first pulse wave and thesecond pulse waves is minimized

The pressure waveform analyzing unit 50 transmits the waveforms of thefirst pulse wave or the second pulse wave and various calculationresults to the display unit 60.

The display unit 60 displays various waveforms or various calculationresults received from the pressure waveform analyzing unit 50. Thedisplay unit 60 may include, for example, a liquid crystal display. Inaddition, the display unit 60 may be a touch panel which receives asignal for switching display from the outside.

The abnormality notification unit 65 determines whether the venouspressure calculated by the pressure waveform analyzing unit 50 exceeds athreshold value. If it is determined that the venous pressure exceedsthe threshold value, this fact is notified. Such a notification to auser may be made by displaying, on a display unit 60, an indication forindicating abnormality along with the measured venous pressure value, orby transmitting a notification for abnormality along with the measuredvenous pressure value to other devices.

The threshold value may be set to a general numerical value used when asurgeon determines the abnormality in clinical practice.

FIG. 2 is a flowchart showing a process of measuring the mean venouspressure by the venous pressure measurement apparatus according to anembodiment.

The first pressure control unit 30a and the second pressure control unit30b set, to 0 mmHg (S200), the pressure (hereinafter, referred to as a“first applied pressure”) applied to the upper arm 101 in the vicinityof the axillary region by the first cuff 20a attached to the proximallocation and the pressure (hereinafter, referred to as a “second appliedpressure”) applied to the upper arm 101 by the second cuff 20b attachedto the distal location with respect to the heart.

The first pressure control unit 30a and the second pressure control unit30b increase the first applied pressure and the second applied pressure,respectively, by a predetermined magnitude (S201). Here, thepredetermined magnitude as a pressure increment may be set, for example,to 10 mmHg. Although the magnitudes of the first applied pressure andthe second applied pressure are set to the same value according to thepresent embodiment, different values may be set.

The first pulse wave is measured by using the first cuff 20a and thefirst pressure sensor 40a, and the second pulse wave is measured byusing the second cuff 20b and the second pressure sensor 40b at the sametime (S202). The pressure waveform analyzing unit 50 calculates thecorrelation between the first pulse wave and the second pulse wave(S203).

FIG. 3 shows graphs of pulse waves in the proximal and distal locationswith respect to the heart in the upper arm and subtraction waveformsthereof. Here, the abscissa axis denotes the elapsed time, and theordinate axis denotes the amplitude of the pulse wave. In addition, theamplitude is indicated as a value obtained by subtracting the centralvalue (DC component) from each pulse wave.

FIG. 3 shows the first pulse wave (proximal pulse wave) and the secondpulse wave (distal pulse wave) obtained when the first applied pressureand the second applied pressure are changed from 10 mmHg to 50 mmHg, andwaveforms obtained by subtracting a correlation component of the secondpulse wave from the first pulse wave on a 10 mmHg basis.

The correlation between the first pulse wave and the second pulse wavecan be calculated by obtaining the subtraction waveform by subtractingthe second pulse wave in the distal location of the upper arm from thefirst pulse wave in the proximal location of the upper arm with respectto the heart. If the amplitude of the subtraction waveform increases,the correlation decreases. If the amplitude decreases, the correlationincreases. Here, in the graphs of FIG. 3, phase correction for matchingthe phases between the first pulse wave and the second pulse wave ismade considering the time during the pressure pulse wave propagates fromthe first cuff 20a to second cuff 20b. Concretely, the time taken fortransmitting the pressure pulse wave from the first cuff 20a to thesecond cuff 20b is set to 40 msec, and the sample data on a 0.1 msecbasis is shifted by a length of 400 samples relatively. In addition, thephase correction may be made by measuring the temporal differencebetween peaks of the first pulse wave and that of the second pulse waveor peaks of differentiated waveforms and removing such a temporaldifference. Furthermore, the correlation between the first pulse waveand the second pulse wave as the applied pressure increases is obtained,and the shift amount having the maximum correlation may be set to theshift amount for the phase correction.

FIG. 4 is a diagram showing a relation between the applied pressure andthe maximum amplitude of the subtraction waveform.

Since the amplitude of the subtraction waveform is maximized when thefirst applied pressure and the second applied pressure are set to 20mmHg, the mean venous pressure may be estimated as 20 mmHg.

It goes without saying that the measurement accuracy can be improved bycorrecting the mean venous pressure estimated in this manner asnecessary. For example, general data regarding a relation between thecuff pressure and intravascular pressure measured using a catheter maybe prepared in advance. The correction may be made by setting theintravascular pressure obtained through comparison with the firstapplied pressure (cuff pressure) when the amplitude of the subtractionwaveform is maximized to the mean venous pressure.

FIG. 5 shows graphs indicating a relation between the first pulse waveand the second pulse wave on the first applied pressure value basis. Theabscissa axis denotes the amplitude of the second pulse wave, and theordinate axis denotes the amplitude of the first pulse wave. In FIG. 5,the contribution ratio R² indicating the correlation between the firstpulse wave and the second pulse wave is showed together. The value R²increases as the correlation between the first pulse wave and the secondpulse wave increases.

The value R² is minimized when the first applied pressure is at 20 mmHg.Therefore, it is apparent that the correlation between the first pulsewave and the second pulse wave is the lowest at this condition.

The venous pressure measurement apparatus 10 increases the first appliedpressure and the second applied pressure (S201), measures the firstpulse wave and the second pulse wave (S202), and calculates thecorrelation between the first pulse wave and the second pulse wave(S203) in an iterative manner until the value R² indicating thecorrelation between the first pulse wave and the second pulse wave isequal to or higher than a predetermined value (NO at S204). Theaforementioned predetermined value may be set to 0.9, for example.

If the value R² is equal to or higher than the predetermined value (YESat S204), the pressure waveform analyzing unit 50 obtains the firstapplied pressure when the value R² is minimized based on the previousmeasurement result (S205). The pressure waveform analyzing unit 50estimates the obtained first applied pressure as the mean venouspressure (S206).

Also, the measurement of the first pulse wave and the second pulse wavemay be terminated at the time when the value R² which is indicates thecorrelation between the first pulse wave and second pulse wavecalculated in step S203 is changed from a decrease to an increase, andthe first applied pressure when the value R² is minimized until thattime may be estimated as the mean venous pressure.

The venous pressure measurement apparatus in an embodiment measures themean venous pressure by estimating that the cuff pressure when thecorrelation between pulse waves in the proximal and distal locationswith respect to the heart is minimized is the mean venous pressure. Thisis equivalent to the case where the venous pulse wave component isextracted from the proximal pulse wave with reference to the distalpulse wave with respect to the heart, and the cuff pressure when thevenous pulse wave component is maximized is estimated as the mean venouspressure.

The venous pressure measurement apparatus in an embodiment alsoestimates the venous pressure by using the venous pulse wave caused bysystole and diastole of the right atrium. Therefore, since pressurepropagation of the venous pulse wave from the heart is not hindered evenif congestion occurs due to occlusion of the vein, existence ornon-existence of the congestion does not matter in the measurement.

Using an embodiment of the venous pressure measurement apparatus, byextracting the venous pulse wave and using the change of it, it ispossible to measure the venous pressure using simple instruments whilethe living body is under natural condition.

The venous pressure measurement apparatus in another embodiment will nowbe described. However, overlapping description with the embodimentsalready described will not be repeated.

An embodiment is different from others in that the applied pressure whenthe correlation between the first pulse wave which is a pulse wave inthe proximal location with respect to the heart and the second pulsewave which is a pulse wave in the distal location is minimized isestimated as the mean venous pressure in the first embodiment, whereasthe applied pressure when the amplitude of the first pulse wave aftersubtracting the arterial pulse wave component from the first pulse waveis maximized is estimated as the mean venous pressure in the presentembodiment.

FIG. 6 is a flowchart showing a process of measuring the mean venouspressure by the venous pressure measurement apparatus.

Similar to the previous process description given in FIG. 2, in stepsS600 to S604, the measurement of the first pulse wave and the secondpulse wave is repeated until the value R² indicating the correlationbetween them is equal to or higher than a predetermined value.

The pressure waveform analyzing unit 50 calculates a slope of theregression expression of the correlation between the first pulse waveand the second pulse wave when the value R² is maximized (S605).

The regression expression is a formula expressing the straight line inthe graph of the relation between the first pulse wave and the secondpulse wave along with the measurement results in FIG. 5. Referring toFIG. 5, the value R² is maximized when the first applied pressure is 40mmHg. The pressure waveform analyzing unit 50 calculates the slope S ofthe regression expression at this condition.

The pressure waveform analyzing unit 50 obtains the arterial pulse wavecomponent of the first pulse wave by multiplying the second pulse waveby the slope S of the regression expression calculated in step S605assuming that the arterial component ratio between the first pulse waveand the second pulse wave is constant (S606). Here, the arterial pulsewave component means a part of the pulse waves, caused by the arterialpulsation.

The pressure waveform analyzing unit 50 extracts the venous pulse wavecomponent of each first pulse wave by subtracting the arterial pulsewave component of the first pulse wave obtained in step S606 from eachfirst pulse wave (S607). Here, the venous pulse wave component means apart of the pulse waves, caused by the venous pulsation.

The pressure waveform analyzing unit 50 obtains the first appliedpressure when the amplitude of the venous pulse wave components of eachfirst pulse wave extracted in step S607 is maximized (S608) andestimates the obtained first applied pressure as the mean venouspressure (S609).

In the venous pressure measurement apparatus according to an embodiment,by extracting the venous pulse wave and using the change of it, it ispossible to measure the venous pressure using simple instruments whilethe living body is under natural condition.

The venous pressure measurement apparatus according to anotherembodiment will now be described.

FIG. 7 is a flowchart showing a process of measuring the mean venouspressure by the venous pressure measurement apparatus according to anembodiment.

The arterial blood pressure is measured based on an oscillometric methodusing the second cuff 20b and the second pressure control unit 30b(S700). Then, the first applied pressure applied to the living body bythe first cuff 20a and the second applied pressure applied to the livingbody by the second cuff 20b are increased to the arterial diastolicpressure (S701). Then, the first applied pressure applied by the firstcuff 20a is successively decreased at a rate of 2 mmHg/s while thesecond applied pressure is maintained at the arterial diastolic pressure(S702), and the first pulse wave and the second pulse wave are measuredrespectively (S703). The measurement is continued until the firstapplied pressure is decreased to be equal to or lower than 5 mmHg (NO atS704).

If the first applied pressure is equal to or lower than 5 mmHg (YES atS704), the venous pulse wave component is extracted from the first pulsewave by subtracting the correlation component of a series of secondpulse waves from a series of first pulse waves (S705). Then, the firstapplied pressure when the amplitude of the venous component of theextracted first pulse wave is maximized is obtained (S706). The obtainedfirst applied pressure is estimated as the mean venous pressure (S707).

According to an embodiment, the venous pulse wave component is removedfrom the second pulse wave by pressed closing the vein in a portionwhere the second cuff 20b is installed while the second applied pressureis maintained at the arterial diastolic blood pressure which is higherthan the mean venous pressure. In addition, the venous pulse wavecomponent is extracted from the first pulse wave by subtracting thearterial pulse wave component extracted from the second pulse wave fromthe first pulse wave, and the first applied pressure when the amplitudeof the extracted venous pulse wave component is maximized is estimatedas the mean venous pressure.

In the venous pressure measurement apparatus according to an embodiment,by extracting the venous pulse wave and using the change of it, it ispossible to measure the venous pressure using simple instruments whilethe living body is under natural condition.

FIG. 8 is a block diagram showing the venous pressure measurementapparatus 10 according to another. In FIG. 8, the living body 100 isshown along with the venous pressure measurement apparatus 10, in whichthe first cuff 20a is attached to the axillary region of the living body100, and the photoplethysmographic pulse wave sensor 70 is attached inthe fingertip.

According to an embodiment, the photoplethysmographic pulse wave sensor70 and the photoplethysmographic pulse wave input circuit 80 are usedinstead of the second cuff 20b and the second pressure sensor 40b of thefirst embodiment or the third embodiment. That is, the second pulse wavein the first embodiment and the third embodiment is detected by thephotoplethysmographic pulse wave sensor 70 and the photoplethysmographicpulse wave input circuit 80. Other parts are similar to the firstembodiment or the third embodiment, so overlapping description will notbe repeated.

The photoplethysmographic pulse wave sensor 70 includes a light emittingelement that emits light of a wavelength band absorbed by the hemoglobinand a light receiving element that receives light emitted from the lightemitting element. The photoplethysmographic pulse wave sensor 70 isattached to the fingertip of the living body to detect thephotoplethysmographic pulse wave. The photoplethysmographic pulse wavesensor 70 is attached to the distal location to the first cuff 20a withrespect to the heart. As a result, it is possible to detect the secondpulse wave having a higher percentage of the arterial pulse wavecomponents in comparison with the first pulse wave.

The photoplethysmographic pulse wave input circuit 80 receives theelectric signal of the photoplethysmographic pulse wave from thephotoplethysmographic pulse wave sensor 70, amplifies it to be anappropriate voltage, and outputs it to the pressure waveform analyzingunit 50.

Similar to the first embodiment to the third embodiment, in the venouspressure measurement apparatus according to the present embodiment, byextracting the venous pulse wave and using the change of it, it ispossible to measure the venous pressure using simple instruments whilethe living body is under natural condition.

FIG. 9 is a block diagram showing the venous pressure measurementapparatus 10 according to another embodiment.

As shown in FIG. 9, the venous pressure measurement apparatus 10includes the first cuff 20a, the first pressure control unit 30a, thefirst pressure sensor 40a, the pressure waveform analyzing unit 50, andthe display unit 60. That is, the first embodiment to the thirdembodiment included two cuffs, two pressure control units, and twopressure sensors. However, the venous pressure measurement apparatus 10according to the present invention includes a single cuff, a singlepressure control unit, and a single pressure sensor. Otherconfigurations of the venous pressure measurement apparatus 10 aresimilar to those of the first embodiment, so overlapping descriptionwill not be repeated.

FIG. 10 is a flowchart showing a process of measuring the mean venouspressure by the venous pressure measurement apparatus according to thepresent embodiment.

The arterial diastolic pressure is measured by using the first cuff 20aand the first pressure sensor 40a (S1000). The arterial diastolicpressure can be measured based on a typical oscillometric method.

Then, the first cuff 20a is attached to the upper arm in the vicinity ofthe axillary region, and the first applied pressure applied to the upperarm in the vicinity of the axillary region by the first cuff 20a is setto 0 mmHg using the pressure control unit 30a (S1001). Then, the firstpulse wave is measured by the first cuff 20a and the first pressuresensor 40a, and the first applied pressure is increased by apredetermined increment (S1004). In this manner, the measurement of thefirst pulse wave done by increasing the first applied pressure isrepeated until the first applied pressure reaches the arterial diastolicpressure measured in step S1000 (NO in S1004).

When the first applied pressure is equal to or higher than the arterialdiastolic pressure (YES at S1004), the measurement is terminated, sothat the pulse wave detected by maximizing the first applied pressure isset to a reference pulse wave, the venous pulse wave component isextracted from the first pulse wave by subtracting the arterial pulsewave component extracted from the reference pulse wave from the firstpulse wave, the first applied pressure when the amplitude of the venouspulse wave extracted is maximized is obtained (S1005), and the firstapplied pressure obtained is estimated as the mean venous pressure(S1006).

According to an embodiment, the cuff pressure within a range equal to orlower than the arterial diastolic pressure is applied to the upper armin the vicinity of the axillary region, and the cuff pressure when theamplitude of the pulse wave detected by using the cuff is maximized isobtained by changing the cuff pressure. That is, the mean venouspressure is estimated by detecting the change of the amplitude of thepulse pressure caused by pressing and closing the vein when the cuffpressure reaches the mean venous pressure.

In the venous pressure measurement apparatus according to an embodiment,by using the change of the venous pulse wave, it is possible to measurethe venous pressure using simple instruments while the living body isunder natural condition.

The venous pressure measurement apparatus according to anotherembodiment will be described.

This embodiment is different from the prior described embodiment in thatthe first applied pressure when the amplitude of the pulse wave ismaximized by changing the first applied pressure is estimated as themean venous pressure according to the fifth embodiment, whereas thepulse wave detected by maximizing the first applied pressure is set to areference pulse wave, and the first applied pressure when thecorrelation between the reference pulse wave and the pulse wave isminimized is estimated as the mean venous pressure according to thesixth embodiment. Other parts of the present embodiment are similar tothe fifth embodiment, so overlapping description will not be repeated.

FIG. 11 is a flowchart showing a process of measuring the mean venouspressure by the venous pressure measurement apparatus according to anembodiment.

Similar to steps S1000 to S1004 of the fifth embodiment, in steps S1100to S1104, the first pulse wave is measured by increasing the firstapplied pressure from 0 mmHg with a predetermined increment within arange equal to or lower than the arterial diastolic pressure.

The pressure waveform analyzing unit 50 stores the data of the measuredfirst pulse wave along with the first applied pressure.

Then, the first pulse wave when the first applied pressure is increasedto the arterial diastolic pressure as the maximum value is set to areference waveform (S1105), and the first applied pressure when thecorrelation between the reference waveform and the pulse wave isminimized is estimated as the mean venous pressure (S1106). Thecorrelation may be obtained as in the first embodiment.

Here, in order to synchronize the first pulse wave with the referencepulse wave, any one of the electrocardiogram and thephotoplethysmographic pulse wave may be used.

In the venous pressure measurement apparatus according to the presentembodiment, by extracting the venous pulse wave and using the change ofit, it is possible to measure the venous pressure using simpleinstruments while the living body is under natural condition.

Although the venous pressure measurement apparatus according to theembodiments of the invention have been described hereinbefore, thisinvention is not limited to above-mentioned embodiments.

For example, although the pulse wave is measured by increasing theapplied pressure from 0 mmHg in all of the embodiments excluding thethird embodiment, the pulse wave may be measured by decreasing theapplied pressure from an appropriate pressure. In addition, although thepulse wave is measured by decreasing the applied pressure from thearterial diastolic pressure in the third embodiment, the pulse wave maybe measured by increasing the applied pressure from an appropriatepressure.

What is claimed is:
 1. A venous pressure measurement apparatuscomprising: a first cuff configured to be attached to a first portionincluding a vein and an artery in a living body; a pressure control unitthat changes a first applied pressure applied by said first cuff to saidfirst portion by sending a flow of air to the first cuff; a first pulsewave sensor that detects a first pulse wave from the pressure receivedby said first cuff from said first portion; a second pulse wave sensorconfigured to detect a second pulse wave including at least an arterialpulse wave in a second portion different from said first portion of saidliving body; a pressure waveform analyzing processor, comprising ananalyzing unit that analyzes differences between said second pulse wavedetected by said second pulse wave sensor and said first pulse wavedetected by said first pulse wave sensor as a correlation, which arechanged as said first applied pressure is changed by said pressurecontrol unit; and a venous pressure calculation unit that calculates avenous pressure based on said first applied pressure and a result ofanalysis by said analyzing unit.
 2. The venous pressure measurementapparatus as claimed in claim 1, wherein said venous pressurecalculation unit calculates said venous pressure based on the firstapplied pressure when said correlation is minimized as a result of theanalysis by said analyzing unit.
 3. The venous pressure measurementapparatus as claimed in claim 1, wherein said analyzing unit obtains avenous pressure wave component by subtracting a component correlatedwith said second pulse wave from said first pulse wave.
 4. The venouspressure measurement apparatus as claimed in claim 3, wherein thecomponent correlated with said second pulse wave is an arterial pulsewave component of said first pulse wave calculated from an arterialpulse wave component of said second pulse wave and said first pulsewave.
 5. The venous pressure measurement apparatus as claimed in claim3, wherein said venous pressure calculation unit calculates said venouspressure based on said first applied pressure when an amplitude of saidvenous pulse wave component is maximized.
 6. The venous pressuremeasurement apparatus as claimed in claim 1, wherein said first cuff isconfigured to be attached to an upper arm in the vicinity of a neck oran axilla.
 7. The venous pressure measurement apparatus as claimed inclaim 1, wherein said second pulse wave sensor is a second cuffconfigured to be attached to said second portion distal to said firstcuff with respect to the heart of said living body, and said pressurecontrol unit further controls a second applied pressure applied by saidsecond cuff to said second portion.
 8. The venous pressure measurementapparatus as claimed in claim 7, wherein said first cuff is configuredto be attached to an upper arm in the vicinity of an axilla, and saidsecond cuff is configured to be attached to a portion distal to saidfirst cuff with respect to the heart in the upper arm where said firstcuff is attached.
 9. The venous pressure measurement apparatus asclaimed in claim 1, wherein said second pulse wave sensor is aphotoplethysmographic pulse wave sensor.
 10. The venous pressuremeasurement apparatus as claimed in claim 7, wherein said pressurecontrol unit controls such that said first applied pressure of saidfirst cuff is equal to said second applied pressure of said second cuff.11. The venous pressure measurement apparatus as claimed in claim 7,wherein said pressure control unit maintains said second appliedpressure constant at a pressure equal to or higher than a venouspressure anticipated in advance.
 12. The venous pressure measurementapparatus as claimed in claim 1, wherein the pressure waveform analyzingprocessor, further comprises a phase correction unit that performscorrection to reduce a phase difference between said first pulse waveand said second pulse wave.
 13. The venous pressure measurementapparatus as claimed in claim 7, further comprising: a third cuffconfigured to be attached between said first cuff and said second cuffwhich are each configured to be attached to the same upper arm tomeasure an arterial pressure, wherein these three cuffs are integratedinto a single unit.
 14. The venous pressure measurement apparatus asclaimed in claim 1, wherein said venous pressure calculation unitcorrects the calculated venous pressure by a relation between saidvenous pressure measured in advance and said first applied pressure. 15.A venous pressure measurement apparatus comprising: a cuff configured tobe attached to a portion including a vein and an artery in a livingbody; a pressure control unit that changes an applied pressure appliedby said cuff to said portion; a pressure sensor that detects a pulsewave from a pressure received by said cuff from said portion; and ananalyzing circuit that calculates a venous pressure based on the appliedpressure and the pulse wave, which is changed as the applied pressure ischanged by said pressure control unit, detected by the pressure sensor;wherein calculating the venous pressure includes comparing a referencepulse wave detected by said pressure sensor when a reference pressurehigher than a venous pressure anticipated in advance is set to saidapplied pressure and said pulse wave detected by said pressure sensorwhen a pressure lower than said reference pressure is set to saidapplied pressure.
 16. A venous pressure measurement method comprising:changing an applied pressure applied by a cuff, which is attached to aportion including a vein and an artery in a living body, to saidportion; detecting a pulse wave from a pressure received by said cufffrom said portion; and calculating a venous pressure based on theapplied pressure and the detected pulse wave which is changed as theapplied pressure is changed; wherein the calculating the venous pressureincludes comparing a reference pulse wave detected when a referencepressure higher than a venous pressure anticipated in advance is set tosaid applied pressure and said pulse wave detected when a pressure lowerthan said reference pressure is set to said applied pressure.